Heretofore, in image pickup optical systems of digital cameras and the like required to be compact and have a high zoom ratio, a four-group zoom lens having a relatively high zoom ratio of about 5× has been known.
Further, despite having a zoom ratio of about 3×, a three-group zoom lens with an intention to further reduce the size by reducing the number of lenses has also been known as described, for example, in U.S. Pat. Nos. 6,452,729, 6,618,210, and Japanese Unexamined Patent Publication No. 2003-307677.